The Commission on Isotopic
Abundances and Atomic Weights (II.1) met for two days, on 10-11
August 2005, during the 43rd IUPAC General Assembly in Beijing. Following
its meeting, the Commission released the changes to the standard atomic
weights, Ar(E), of 16 chemical elements. The following
changes are based on new determinations of isotopic abundances and reviews
of previous isotopic abundances and atomic masses:

From

To

Aluminium

26.981
538 (2)

26.981
5386 (8)

Bismuth

208.980
38 (2)

208.980
40 (1)

Caesium

132.905
45 (2)

132.905
4519 (2)

Cobalt

58.933
200 (9)

58.933
195 (5)

Gold

196.966
55 (2)

196.966
569 (4)

Lanthanum

138.9055
(2)

138.905
47 (7)

Manganese

54.938
049 (9)

54.938
045 (5)

Neodymium

144.24
(3)

144.242
(3)

Phosphorus

30.973
761 (2)

30.973
762 (2)

Platinum

195.078
(2)

195.084
(9)

Samarium

150.36
(3)

150.36
(2)

Scandium

44.955
910 (8)

44.955
912 (6)

Sodium

22.989
770 (2)

22.989
769 28 (2)

Tantalum

180.9479
(1)

180.947
88 (2)

Terbium

158.925
34 (2)

158.925
35 (2)

Thorium

232.0381
(1)

232.038
06 (2)

The values are
presented in a concise notation whereby the standard uncertainty is
given in parenthesis next to the least significant digits to which
it applies; for example, Ar(Al) = 26.981 538 (2)
is the concise form of the expression Ar(Al) = 26.981 538 ± 0.000 002

These changes in the atomic weights will be published in a new Table
of Standard Atomic Weights 2005, which will be submitted for publication
in Pure and Applied Chemistry* by the end of 2005. The commission
also continued its review of publications of variations in the natural
isotopic abundances. For more details about the Commission meeting in
Beijing, see Chem.
Int.
Nov/Dec 2005 issue, Division Roundups on p. 7, or contact Michael
E. Wieser <mwieser@ucalgary.ca>,
secretary of the Commission.